Shock absorber with retractable stroke for airplanes



R. L. LEVY. 2,554,581 saocx ABsoRBER wrm REmcTABu-z STROKE. Foa AIRPLAm-:s

May 29, 1951 A2 Sheets-Sheet 1 Filed May 1946 ils R. L. LE/vY May 29, 1951 SHOCK ABSORBER WITH RETRACTABLE STROKE FOR AIRPLANES Filed May 27. 1946 2 Shee/ts-Shheet 2 Patented May 29, 1951 SHOCK ABSORBER WITH RETRACTABLE STROKE FOR AIRPLANES Ren Lucien Levy, Paris, France, assgnor to Societe dInventions Aeronautiques et Mecaniques S. I. A. M., Geneva, of Switzerland Switzerland, a corporation Application May 27, 1946, Serial No. 672,509 In France July 31, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires July 31, 1961 11 Claims.

The present invention relates to contractable oleo-pneumatic shock absorbing struts for retractable landing gear.

More particularly, the invention relates to such a strut including a cylinder and in which liquid contained between two interconnected pistons that are movable in the cylinder traverses upon movement of the pistons small passages in a diaphragm that is ixed to the Cylinder between the pistons with a gas under pressure exerting shock absorbing action above the upper piston.

In this type of arrangement when it is desired to contract such a strut in order to retract the landing gear, the two pistons are raised in their common cylinder by overcoming the pressure which exists above the upper piston and which operation necessitates a considerable expenditure ci energy.

IThe present invention therefore has for an object to provide a shock absorbing strut of this character in which the contraction is effected without substantially compressing the gas situated above the upper piston.

According to the invention the two pistons instead of being interconnected for simultaneous movement as is the common practice are united one to the other by a traction rod secured to one of the pistons and which, during contraction of the strut corresponding to the retraction of the ianding gear, slides in the interior of the other piston, while the excess liquid that is enclosed between the two pistons is permitted to escape.

The main features of the strut in accordance with the invention, therefore, are as follows:

l. The rod of the upper piston traverses the lower piston and enters into a chamber formed in a hollow rod for the lower piston and terminates within the chamber in a flange or a head;

2. It is the liquid pressure acting on the lower surface of the lower piston for effecting contraction which controls the opening of a valve permitting the evacuation of the excess liquid which is contained between the two pistons;

3. This excess liquid thus evacuated or owing from the space compressed between the two pistons is collected in an accumulator, and re-used, therefore assuring the subsequent expansion of the strut.

In a first embodiment of this invention this accumulator is disposed exteriorly of the strut.

In a second embodiment the accumulator is integrated with the strut, the hollow rod of the lower piston being so formed as to provide the two chambers, preferably concentric, one of which is in permanent communication with the space between the two pistons and the other chamber constituting the accumulator which receives during retraction of the gear and contraction of the strut the excess liquid expelled from the nrstementioned chamber.

In the following specification reference is made by way of example to the attached drawings, in which:

Figure l is a diagrammatic view of a first embodiment of a contractable oleo-pneumatic shock absorbing strut accordingfto the invention;

Figure 2 is a diagrammatic view of a second embodiment; and.

Figure 3 is a diagrammatic view of a third embodiment.

With reference to Figure l, the strut comprises a cylindrical body I in which is mounted a lower piston 2 the rod 3 of which is hollow. The cylinder I is attached or pivoted to the fuselage or other structural part of the aeroplane by a lug 4 and the hollow piston rod 3 is connected to the rolling gear by a lug 5 carried on theY rod 3. The piston 2 is traversed by a central bore or channel 6 which communicates at one end with the chamber 'I constituting the hollow portion of the rod 3 and at its other end with a compartment or chamber 8 formed between piston 2 and xed diaphragm 9 disposed transversely of the cylinder I. The diaphragm 9 is provided with a central opening Il! through which passes the rod II of a small or upper piston I2 placed in an upper gas containing chamber I3 formed at the top' of the cylinder I. This rod II traverses the chamber 8 and the bore or channel 6 in the head of the piston 2 and terminates within the chamber l in a circular head or flange I4 of a greater diameter than that of the channel 6 so that while piston 2 can move relative to rod II in sliding relationship the two elements are maintained in this slidable or telescopic relationship. The diaphragm 9 is further provided with orifices I5 controlled by valves I6 and I6 working in opposite directions. The hollow piston rod 3 traverses the bottom I'I` of the cylinder I and fluid tgihtness is assured by the provision of a packing I8. The piston 2 is further provided with packing indicated at I S and 2l).y Within the lower portion of the cylinder I and beneath the piston 2 is provided an abutment 2I which restricts the movement of the piston 2 toward the bottom of the cylinder I. As previously indicated, the upper chamber I3 is filled with gas under pressure.

Between the upper surface of the diaphragm 9 and the lower surface of the piston I2 is provided a chamber 22 which is connected kthrough with. In chamber 28 is movable a free plunger orpiston 29 which is subjected to the action of a calibrated spring 30 bearing against the partition 28. The numeral 3iV denotes apertures in the partition 26, the passage of fluid through which is controlled by the valve 32. The stem 33 of this valve which traverses a central bore or guide 34 axially of the partition 2B is moved by the movement of the plunger 29 toward partition 26 when the plunger is moved with suicient force to overcome the action of the spring 3D. A chamber 35 is provided in the rear or rem-cte end of the box 24 behind the plunger 29 and communieating with this chamber is a tube 33 which is in communication with a tube 31, one end of which communicates with a chamber 38 formed between the bottom of cylinder l and the lower surface of piston 2 and the other end communicating with a distributor pump device indicated at 39. From the distributor 39 a pipe 40 provides communication with the valve box 24. Mounted in communication with this pipe 4B is an oleo-pneumatic accumulator 4I. The distributor pump devicel 39 is constituted by a double-acting pump comprising two cylinders 42 and 43 arranged side by side and in which pistons 44 and 45 are respectively movable. The rods 415l and 41 of these pistons are united through a yoke 48 connected with an operating lever 49. At the bottom 5@ of the two cylinders 42 and 43 are provided admission valves 5I and 52, respectively, and exhaust vvalves 53 and 54, respectively. The pipe 40 is divided into two branches 55 and 56 communicating through admission valves 5I and 52 with cylinders 42 and 43 and the pipe or tube 31 is vdivided into branches 51 and 58 communicating through exhaust valves 53 and 54 with the respective cylinders. A by-pass 59 interconnects pipes 31 and 43 adjacent the distributor device and the by-pass is controlled by valve 38 operated by handle 6I carried on the lever 49 through a suitable mechanical connection illustrated diagrammatically at 62.

The operation of the strut shown in Figure 1 is asfollows:

In normal condition the valves 32 and 6B are closed, the shock absorber then functioning in its customary manner. Pistons 2 and I2 move in unison by reason of the incompressibility of the liquid filling chambers 22, 8 and 1. When it is desired to contract the strut lever 49 is reciprocated to and fro while pressing on handle 6I. Upon this operation the pump sucks liquid from the accumulator 4I and delivers it under increasing pressure into pipe 31, this liquid under pressure passing through tube 36 and communicating with valve box 24 behind the plunger or piston 29, thereby pushing the plunger 29 against the action of spring 3i! thus pushing valve stem 33 and opening valve 32. Simultaneously fluid ventering chamber 38 causes piston 2 to rise and therebyrcontract the landing gear. The liquid contained in chamber 8 is forced by piston 2 into chamber 22 thence into chamber 21 and through pipe 4 0 into accumulatorM. The upward movement of piston 2 does not effect piston l2. Therefore, the contraction of the strut takes place'in such a manner that the gas contained in chamber I3 ,isl not substantially compressed beyond itsnormal working pressure. Thus energy normally utilized in conventional contractable strut arrangements to compress this gas is economized.

In order to expand the strut it is suiicient with lever i9 being stationary to press on handle l. This places pipes d8 and 31 into communication with one another. The pressure in accumulator 4l built up by the preceding pumping operation is then exerted through pipe 4G, valve 32, passage 23, chamber 22, valve I6' and chamber S on the upper side of piston 2 and through pipes 4S, bypass y59, pipe 31 and chamber 38 on the lower side oi this piston. Inasmuch as the surface area of the upper side of the piston receiving pressure of huid from chamber 8 is greater than the surface area on the lower side of -ix at piston 2 through dilerential pressure action the piston 2 is pushed toward the bottom l1 of cylinder I until it is stopped by the abutment or collar 2|.

l`With reference to Figure 2 which illustrates a second embodiment of the contractible strut in accordance with the invention, the strut comprises a cylinder 63 within which is mounted a piston c4 provided with packing S5 and 36. rhe rod 61 of piston 64 is hollow and of large cross sectional area. This rod terminates in lug 68 provided with eye 39 for attachment to the rolling gear. The hollow rod 61 traverses the bottom 1U of the cylinder and uid tightness is assured by means of packing 1l. Piston 54 therefore subdivides the cylinder 63 into a lower annular chamber 12 and an upper chamber 13. This chamber 13 is limited by the provision of a xed diaphragm 14 disposed transversely of the upper portion of cylinder 53 and which diaphragm is provided with -orices 15 and a central orifice which is traversed by a rod 16 of a small or upper piston 11 which in turn subdivides the upper part of cylinder 63 into two chambers 18 and 95. Piston B4 carries a tube 19 which is in communication by oblique passages 3G with chamber 13. Piston 64 also has a central passage or channel 8l through which passes rod 16 of piston 11 and which rod terminates within the tube 19- in a head or ange 82 that cooperates with the lower surface 83 of piston 64 which surface closes the upper part of tube 19. The connection between pistons 11 and 64 is therefore the same as the connection between pistons I2 and 2 in the embodiment shown in Figure 1.

A collar 84 xed within cylinder E3 restrains the descent of piston 54 in a manner Similar to abutment 2l shown in Figure 1. At the lower extremity of tube 13 is an opening to which is connected pipe 85 connected in turn with a distributor pump device similar to that described with reference to Figure 1, but not illustrated in Figure 2. A flexible branch pipe 85 provides coinmunication between pipe S5 and annular chamber 12 of cylinder 63. The lower part of tube "I9 constitutes a valve box functioning similar to the valve box 24 of Figure 1. AS shown, a valve 86 is adapted to close orices 81 of partition 88 fixed within tube 19. The axis of the stem 39 of Valve 85 is guided within partition 88 and this Stem 89 cooperates with a free plunger or piston 93 closely iitting within lower extremity of tube 19 and subjected on one side to the pressure of liquid issuing from pipe 85 and on the other side to the action of a calibrated spring 9|. An orifice 92 provided in the wall of tube 19 between partition BE and plunger El@ provides for communication between the interior space 53 of tube 19 and the annular space`9 4 between theinner wall of hollow piston rod B? and the outer Wall of tube 19. The chambers 13 and 95 situated respectively between the lower piston and the diaphragm and the diaphragm and the upper piston are filled with liquid and therefore chamber 93 formed within tube '1S is also full of liquid, since it communicates through passage with chamber '13. The lower part of annular chamber 9d also contains a certain quantity of liquid. Above this liquid is a gas under pressure and the introduction of the liquid and gas under pressure into accumulator space Q4 is effected through a pipe 96 provided with valve 96.

The operation of this embodiment is similar to that described with reference to Figure l;

Under normal conditions valve 86 is maintained on its seat by the pressure of the liquid contained in space SS. llhe shock absorber then functions in its customary manner. When it is desired to contract the strut it is only necessary to apply pressure through pipe 35. The liquid under pressure issuing from pipe 85 acts on the lower side of plunger 9S raising the same against the action-of spring Si thereby lifting valve 86 from its seat. Simultaneously iiuid under pressure through branch enters chamber l2 to raise piston 66. This action is effected without difficulty, the liquid contained in chamber 13 ,passing through passages 8U, space 93, open Valve 86 and orifice 92 into the annuar space Se which constitutes an accumulator. The landing gear then contracts. It is to be remarked that this contraction does not require a further compression of the gas which is already under strong pressure contained in chamber lil. the strut it is only necessary to cut oli the pressure developed by the pump in pipe therefore, under the action of the energy accumulated in the annular space 24, the liquid contained in the lower part oi this space returns to chamber i3 and piston 61S is moved downwardly to its normal position of operation due to a pressure differential as described in connection with Figure 1.

In the modification shown diagrammatically in Figure 3 the shrinkage of the telescopic strut 63-61 is coincident with the retraction oi the landing gear and is effected by mechanical traction on lug 6E by means of a cable 98 in the manner shown and described in my prior Patent No. 2,294,915, issued September 8, 1942, the hydraulic pressure in this case being applied on the lower side of piston 90 through pressure line 85.

What I claim as my invention and desire to secure by Letters Patent is:

l. A contractable oleo-pneumatic shock absorbing strut for retractable landing gear, comprising a cylinder, two interconnected pistons movable in said cylinder, an apertured diaphragm iixed to said cylinderbetweenthetwo pistons, a gas under pressure in the cylinder and exerting shock-absorbing action above the upper piston, a strut which cornprises a hollow rod fixed to one of said pistons; a traction rod iixed to the other piston and slidable in said hollow rod te elfect the contraction of the strut, said cylinder being lled with liquid beneath the upper piston and the liquid upon movement of the pistons passing through the diaphragm; and means to allow for the escape of excess liquid from the space between the two pistons during said contraction.

2. A contractable shock-absorbing strut for retractable landing gear comprising: a cylinder; a xed diaphragm subdividing this cylinder into an To extend upper and a lower chamber; a first piston subdividing said upper chamber into a chamber filled with gas under pressure and a chamber filled with liquid; a second piston, subdividing said lower chamber into two chambers filled with liquid, and having a hollow rod traversing the bottom of the cylinder and projecting below said bottom to carry the landing gear and a traction rod secured to the iirst piston, traversing said diaphragm and said second piston and ending in a head working in a chamber formed in the hollow rod of said second piston.

3. A contractable oleo-pneumatic shock-absorbing strut for retractable landing gear, which comprises: a cylinder; a fixed diaphragm subdividing this cylinder into an upper and a lower chamber; a iirst piston subdividing said upper chamber into a chamber iilled with gas under pressure and a chamber filled with liquid; a second piston having a hollow rod and subdividing said lower chamber into two chambers lled with liquid; a telescopic mechanical connection between said two pistons; pressure means capable of acting under the second piston to contract the strut; an'outlet for the escape of excess liquid from the chambers between the two pistons during said contraction; and a valve controlling said outlet and controlled by said pressure means.

4. A contractable oleo-pneumatic shock-absorbing strut for retractable landing gear, which comprises: a cylinder; a fixed diaphragm subdividing this cylinder into an upper and a lower chamber; a nrst piston subdividing said upper chamber into a chamber lled with gas under pressure and a chamber filled with liquid; a second piston having a hollow rod and subdividing said lower chamber into two chambers filled with liquid; a telescopic mechanical connection between said pistons; pressure means capable of acting under the second piston to contract the strut; an .outlet for the escape of excess liquid from the chambers between the two pistons during said contraction; a Valve controlling said outlet and controlled by said pressure means; and an oleo-pneumatic accumulator to receive said excess liquid, and to effect the extension of the strut with the aid of a pressure differential established between the two opposite faces of said second piston.

5. A contractable oleo-pneumatic shock-absorbing strut for retractable landing gear, which comprises: a cylinder; a fixed diaphragm subdividing this cylinder into an upper and lower chamber; a first piston subdividing said upper chamber into a chamber lled with gas under pressure and a chamber filled with liquid; a second piston having a hollow rod and subdividing said lower chamber into two chambers filled with liquid; a telescopic mechanical connection between said two pistons; pressure means capable of acting under the second piston to contract the strut; an outlet for the escape of excess liquid from the chambers between the two pistons during said contraction; an exterior valve controlling said outlet and controlled by said pressure means; an exterior oleo-pneumatic accumulator to receive said excess liquid; and means, controlled by said accumulator to effect the extension of the strut.

6. A contractable oleo-pneumatic shock-absorbing strut for retractable landing gear, which comprises: a cylinder; a fixed diaphragm subdividing this cylinder into an upper and a lower chamber; a iirst piston subdividing said upper chamber into a chamber filled with gas under pressure and a chamber lled with liquid; a second piston having a hollow rod and subdividing said lower chamber into two chambers lled with liquid; a telescopic mechanical connection between said two pistons; pressure means capable of acting under the second piston to contract the strut; an outlet for the escape of excess liquid from the chambers between the two pistons during said contraction; a valve inside said hollow rod for controlling said outlet and controlled by said pressure means; an oleo-pneumatic accumulator likewise inside said hollow rod to receive said excess liquid; and means, controlled by said accumulator, to effect the extension of the strut.

7. An contractable shock-absorbing strut for retractable landing gear comprising: a cylinder; a xed diaphragm subdividing this cylinder into an upper and a lower chamber; a first piston subdividing said upper chamber into a chamber filled with gas under pressure and a chamber filled with liquid; a second piston,'subdividmg said lower chamber into two chambers lled with liquid, and having a hollow rod traversing the bottom of the cylinder and projecting below said bottom to carry the landing gear; a traction rod secured to the rst piston, traversing axial passages provided in said diaphragm and in said second piston, respectively, and ending in a head working in the hollow rod of said second piston; and exterior means adapted to contract and extend the strut, respectively.

8. Strut according to claim 7 in which the means to contract and extend the strut comprises: a pump; an oleo-pneumatic accumulator; a valve-box; a pressure line connecting said pump to the chamber under the second piston; a branch of said pressure line connecting said pump to said valve-box; a return line connecting said valvebox, said accumulator and said pump; and a passage between the chamber under the rst piston and said valve-box.

9. A contractable shock-absorbing strut forv retractable landing gear comprising: a cylinder; a piston having a hollow rod projecting through the bottom of said cylinder; a tube in the axis of said rod; a pressure line in communication with the bottom of the annular chamber comprised between said piston and said bottom of the cylinder, and with the bottom of said tube, respectively; means to feed air and liquid in the annular space between said tube and said hollow rod;

a valve in the bottom of said tube; and a passage between said bottom of the tube and said annular space.

1G. A contractable shock-absorbing strut for retractable landing gear comprising: a cylinder; a piston having a hollow rod projecting through the bottom of said cylinder; a tube in the axis of said rod; a pressure line in communication with the bottom of said tube; means to feed air and liquid to the annular space between said tube and said hollow rod; a valve in the bottom of said tube under the control of said pressure line; a passage between said bottom of the tube and said annular space; and mechanical traction means to contract the strut upon retraction of the landing gear.

l1. A contractable oleo-pneumatic shock absorbing strut for retractable landing gear including a cylinder, a diaphragm within and xed to said cylinder and dividing the same intoupper and lower compartments, said diaphragm having restricted passages therethrough, a piston in each compartment and respectively disposed on opposite sides of the diaphragm, resilient means above the piston in the upper compartment and dening shock absorbing means for the landing gear, said cylinder being filled with liquid below said upper piston, connecting means between the pistons permitting axial movement thereof relative to each other, said lower piston carrying a strut extending through the cylinder and having means thereon to carry the landing gear, means to contract the strut, said contracting means eecting movement of the lower piston relative to the upper piston, and means communicating with the cylinder to allow escape of excess liquid from the space between the pistons during contraction.

RENE' LUCIEN LEVY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,186,266 Onions Jan. 9, 1940 2,392,892 Ward Jan. 15, 1946 FOREIGN PATENTS Number Country Date 839,099 France Dec. 26, 1938 

